Do I need to verify domain? And what will go wrong if I haven't?

When I create Services IDs for my website for Sign in with Apple, I was asked to verify my domain by putting a file into specific path https://example.com/.well-known/apple-developer-domain-association.txt


My question is, what would happen if I don't do that? I'm testing it right now and it seems to work without verifying the domain.

Do I need to verify domain? And what will go wrong if I haven't?
 
 
Q